The Frobenius number of a1, ..., an is the largest integer b for which the Frobenius equation a1x1+...+anxnb has no non-negative integer solutions. The ai must be positive integers.
If the integers ai are not relatively prime, the result is Infinity.
If one of the ai is the integer 1, then the result is -1.
If b is the Frobenius number of a1, ..., an, then FrobeniusSolve[{a1, ..., an}, b] returns {}.